OPINION: As the issue of transnational terrorism rises to the top of the international security agenda, unmitigated climate change could well succeed it as the defining security challenge of the 21st century unless measures are taken to substantially slow, then reverse, the unprecedented levels of greenhouse gases being pumped into the Earth’s atmosphere.

This is the inescapable conclusion to be drawn from a close reading of the now voluminous scientific literature on the causes and consequences of climate change compiled by the world’s pre-eminent scientific organisations.

Yet six years after the ignominious failure of the Copenhagen climate summit to achieve its modest goals, and with the successor Paris summit about to start, Australians seem more confused and divided than ever about the causes of climate change and its seriousness.

A recent survey by the CSIRO confirms a nearly decade-long trend showing a steady decline in those who believe recent climate change is caused by humans. Conversely, climate scientists are becoming more confident that ­humans, not natural variability, are responsible. The fact many of those surveyed more than once by the CSIRO during the past five years have changed their positions is an even more telling indicator of public confusion.

The debate over climate change in this country is too narrowly and technically framed, leaving many Australians feeling bewildered and disconnected.

This climate dichotomy is partly attributable to the partisan and ideological nature of the climate change debate in Australia, which has distorted the science and frequently reduces policy discussions to unseemly name-calling between opposing communities of advocates.

At one end of the belief spectrum are “apocalyptic” environmental activists who see every drought or extreme weather event as indisputable evidence of climate change. At the other end are climate change “deniers” who believe there is no global warming or that whatever warming may be occurring is due to natural variability, not humans.

But there is another, less obvious reason. The debate over climate change in this country is too narrowly and technically framed, leaving many Australians feeling bewildered and disconnected. Much of the conversation centres on complicated targets and mechanisms for achieving reductions in greenhouse gas emissions and the virtues, or failings, of various schemes for carbon trading.

While these issues are important, what has been missing is a compelling, science-based national security narrative that provides crucial context for climate-related economic decision-making.

Climate change is not amenable to a simple cost-benefit analysis because it transcends economic calculations. Unmitigated climate change is a genuine national security problem.

If our climate change scientists are right, a substantially warmer planet will have adverse implications for all ­humanity and the stability of ­nation-states that requires judgments about political and strategic risk, as well as economic cost.

One of the seminal strategic lessons of the past 20 years is that national security can be threatened not only by hostile states and conventional armies but also by terrorist non-state actors and non-military transnational forces such as climate change, disease pandemics, resource depletion and unregulated population movements, to name just a few.

Climate change may turn out to be the most serious even if we can keep warming below 2C, the previously agreed threshold for dangerous climate change.

There is considerable evidence that temperature rises already observed are dangerously stressing ecosystems and the coupled built environment on which humans depend for their health, wealth and security.

The immediate problem is the rate at which temperatures are increasing rather than the absolute size of differential warming. Spread across several centuries, or a millennium, temperature rises of several degrees may be managed without political instability or significant threats to commerce, agriculture and infrastructure.

Compressed within the space of a single century, a rapidly warming planet will present far more daunting challenges of human and biological adaptation, especially for natural ecosystems that typically evolve across hundreds of thousands and millions of years.

Climate change and security are linked in many ways. Weather extremes and greater fluctuations in rainfall and temperatures have the capacity to adversely refashion the world’s productive landscape and aggravate food, water and energy scarcities.

Climate change and security are linked in many ways. Weather extremes and greater fluctuations in rainfall and temperatures have the capacity to adversely refashion the world’s productive landscape and aggravate food, water and energy scarcities. Many staple crops, for example, are already near their maximum temperature tolerance and climate change will exacerbate the world’s looming fresh water shortages.

More extreme weather patterns will result in greater death and destruction from natural disasters, adding to the burden on poorer countries and stretching the resources and coping ability of even the most developed nations, as Hurricane Katrina proved when it devastated New Orleans in 2005, causing about $US125 billion in economic damage, making it the worst natural disaster in US history.

Once-in-100-year storms could well become common weather events along with desiccating heatwaves.

Even if not catastrophic in themselves, the cumulative impact of rising temperatures, sea levels and more mega droughts on agriculture, fresh water and our energy system could fatally weaken already fragile states, contributing to destabilising internal conflicts and, in some cases, their eventual collapse.

Where climate change coincides with other transnational challenges to security, such as terrorism or pandemic diseases, or adds to pre-existing social tensions, then the impact will be magnified. In effect, climate change will be a threat multiplier.

These are not the wild imaginings of radical greens but the considered view of most governments and, increasingly, their hard-headed military and national security establishments.

In 2008, the US National Intelligence Council judged that “global climate change will have wide-ranging implications for US national security interests during the next 20 years”.

Testifying before congress last year, a senior US Defence official justified the inclusion of climate change in the latest quadrennial review — the equivalent to Australia’s defence white paper — by arguing that “the effects of climate change will have serious implications for the department’s ability to maintain both its infrastructure and the landscape around it, and to ensure military readiness in the ­future”. The 2015 US national security strategy maintains that climate change is “an urgent and growing threat to our national security, contributing to increased natural disasters, refugee flows, and conflicts over basic resources”.

Europeans regard climate change as a first-order foreign policy and national security problem on a par with terrorism and the proliferation of weapons of mass destruction. Since former British foreign secretary Margaret Beckett convened the first debate in the UN Security Council on climate change in 2007, virtually all European leaders have accepted that unmitigated climate change will have profound consequences for European and global security. The 2008 British national security strategy, for example, says “climate change is potentially the greatest challenge to global stability and security, and therefore to national security”.

Australia generally has followed European and North American trends in designating climate change as a security problem. Following a classified review by the Office of National Assessments, Australia’s premier intelligence agency, of the climate change threat to national and international security, climate change was listed as a major security challenge in the 2008 national security statement and as a broader global challenge with national security implications in the 2013 national security strategy.

Tony Abbott’s well known climate change scepticism meant the wider security dimensions were largely ignored during his tenure as prime minister.

Turnbull could usefully draw on the national security approach to risk management, which typically evaluates and prioritises security challenges by weighing the likelihood of a threat against its impact.

But with his departure, and that of fellow sceptic Canadian prime minister Stephen Harper, it’s hard to find a Western leader who identifies with their position.

However, Abbott’s departure is unlikely to heal the rift between his fellow sceptics and most Australians who believe climate change is a serious problem. Nor will it dissipate public confusion about the science without an authoritative government restatement of the main conclusions reached by the world’s leading climate scientists.

This is easier said than done because some climate change contrarians have cast doubt on the mainstream science by disputing the credentials and findings of the influential Intergovernmental Panel on Climate Change and by challenging the notion there is an expert, scientific consensus on climate change.

So what exactly is the IPCC, what are its key scientific findings and how plausible are the arguments of its critics?

Established in 1988 as a partnership between the World Meteorological Organisation and the UN Environment Program, the IPCC is charged with assessing the scientific literature to state definitively what we know and don’t know about climate change. The IPCC also reviews national and international climate change policy and conducts scientific assessments based on peer-reviewed and published literature.

The several thousand contributors to this process represent the cream of the world’s climate change scientists and their collective judgments are published every five to seven years. Rather than making one definitive assessment, several plausible emission scenarios are developed from which likely climate change impacts are extrapolated.

They, and the accompanying summaries for policymakers, are exhaustively reviewed, then scrutinised and endorsed by all UN member states. So the IPCC’s assessments are, in effect, the considered view of the international community.

In the Fifth Assessment Report, published last year, the IPCC says the warming of the climate system is “unequivocal” and that “since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.” Moreover, the cause of this warming is “extremely likely” (at least 95 per cent probability) to have been caused mainly by ­humans.

Although nothing is absolutely certain in this world, other than death and taxes, it’s difficult to think how much more certain one can be that the Earth is rapidly warming and that we are largely responsible.

However, critics have attempted to rebut these findings by ­attacking the credibility of the IPCC, accusing the organisation of manipulating climate change data, fraud and reflecting “a culture of corruption”. Paradoxically, they have been assisted in their aims by some sloppy IPCC editing and the occasional use of papers by environmental activists to support research conclusions that should have failed the objectivity test.

Critics had a field day in 2010, when several controversies involving the IPCC and well-known climate change scientists became front page news and appeared to lend credence to the critics’ claims, undermining public confidence in the IPCC and climate science more generally.

The most significant of these, dubbed Climategate, Glaciergate and Amazongate by the media, evoked memories of the unsavoury Watergate burglary that eventually brought down US president Richard Nixon.

The Climategate controversy began when hackers exposed more than 1000 private emails sent between a leading US climate scientist from Pennsylvania State University, Michael Mann, and colleagues at Britain’s East Anglia Climatic Research Unit. Critics touted the emails as evidence climate change scientists deliberately had invented or manipulated the data and conspired to prevent the publication of research contradicting their own.

A few months later, the IPCC received another blow when it was revealed that a claim in one of its benchmark reports that the Himalayan glaciers would melt by 2035 because of global warming was based on speculation by an ­obscure Indian scientist.

Hard on the heels of Glaciergate came Amazongate, so called because the IPCC made reference to an assertion in another of its publications that 40 per cent of the Amazon rainforest could be wiped out by a small reduction in rainfall. This was shown to be an inaccurate extrapolation from a report written by two environmental ­activists that lacked the requisite data to justify such a conclusion.

Yet subsequent independent investigations into each of these controversies established conclusively that these were failures of procedure, not of the science. The Associated Press thoroughly vetted all 1073 of the Climategate emails and found there was no substance to the claim the data had been manipulated. Neither Climategate nor any of the other “gates” contradicts the IPCC’s central conclusion that global warming is largely due to human activity.

What of the criticism that there is widespread disagreement among experts about the fundamental science underpinning the IPCC assessments and that there is no scientific consensus on climate change?

It is true there are dissident voices in the scientific community on some aspects of climate change. But consensus does not mean unan­imity. Climate scientists, like those in any discipline of science, are constantly testing and revalidating their assumptions and findings. So there will naturally be disagreements along the path to enlightenment. But it would be wrong to interpret this healthy dialectic as a major schism in the discipline. In reality, very few scientists reject the IPCC’s core judgment that human activities are causing the planet to warm rapidly. Most of those who do are not specialists in climate science.

How do we know this? Reviews of the expert literature show that 97 per cent of climate researchers actively publishing climate papers endorse the consensus position.

No scientific body of international standing maintains a formal position dissenting from the main findings of the IPCC. The last holdout was the American Association of Petroleum Geologists. It joined the consensus in 2010 when its own executive committee declared: “Climate change is peripheral to our science … AAPG does not have credibility” in the field of climate science.

The most eminent and authoritative scientific and technical ­organisations are generally considered to be the world’s national science academies. All those of major nations support the consensus view including the US, Japan, China, Russia, Mexico, Brazil, India, Germany and France, as does our own Academy of Science.

The problem is not lack of scientific consensus or scientific confidence in the judgments of the IPCC but, rather, a failure to communicate effectively the science to a confused public and policymakers.

As an effective communicator, and a supporter of the scientific consensus, Malcolm Turnbull has the opportunity provided by the Paris summit to initiate a more constructive and informed public discussion about the importance of climate change that can help bridge the ideological divide within his own party and address the knowledge gap between climate scientists and the public.

This will not be easy and entails a degree of political risk. But the benefits are potentially greater. Any reduction in ideology and emotion on climate change will strengthen Turnbull’s position in the party, make it more difficult for Labor to exploit internal Coalition tensions on the issue, improve policy outcomes and build public support for the substantial reductions in greenhouse gases that are necessary to slow the rate of warming.

The key to success is to better articulate the scientific consensus within a broader national security narrative that makes a more compelling case for action by setting out the likely consequences and costs of allowing temperatures to rise beyond 2C.

Climate change is essentially a risk-management problem. Framing it in these terms may help to win over some of the sceptics because it does not require them to relinquish their scepticism, only to accept that there is a need to hedge against the possibility their scepticism may be misplaced.

Turnbull could usefully draw on the national security approach to risk management, which typically evaluates and prioritises security challenges by weighing the likelihood of a threat against its impact. Climate change would rate high on both measures and even higher if emissions were not brought down quickly.

He also might look at how the insurance industry evaluates climate change risk. Actuaries are among the most skilled calculators of risk for the simple reason that an insurance company will not survive if premiums don’t accurately reflect the real level of risk. Unsurprisingly, insurance premiums on climate change are rising because the empirical evidence supports the likelihood of significant and widespread impacts from temperature increases, sea level rise and more extreme weather events such as cyclones, bushfires, floods and heatwaves.

Given that the weight of scientific opinion is heavily supportive of the IPCC assessments, only the imprudent would bet on a benign climate future or that the risk can be managed solely by adaptation.

As pointed out by Bjorn Lomborg in Inquirer earlier this month, the carbon reduction targets committed ahead of the Paris summit will cut temperatures by just 0.05C. Unless there are substantial further cuts to emissions in the critical next 10 to 15 years, then the more extreme climate change scenarios become distinct possibilities rather than low probabilities.

A proper risk-based approach must include the possibility that climate change scientists actually may have underestimated the rate of warming because of their innate conservatism and the relatively high level of certainty required in reaching scientific consensus — far higher than is customary in the national security community.

A salient example is the rapid warming of the icy polar regions, which act as the world’s airconditioners.

This is a particular problem in the northern polar region where glaciers, and the ice cap itself, seem to be melting faster than climate scientists had anticipated, including the massive ice sheet covering Greenland.

The rate of ice cap and glacial melt is important for two reasons. Less ice means less heat radiated back into space and therefore even higher temperatures. And accelerated melting of polar ice would dramatically raise the estimates of sea level rise and the impact on vulnerable coastal areas and small island states.

If the ice on Greenland disappears entirely, sea levels will be 4m to 6m higher by the end of this century.

The message that Turnbull should deliver is that the more we can reduce carbon and other greenhouse gas emissions, the lower the risk of dangerous climate change outcomes. The higher these emissions, the greater will be the changes to our climate, calling into question our ability to adapt and avoid widespread species loss, water and food insecurity, energy disruptions, increased refugee flows, infrastructure failure and more conflicts.

If he can do this effectively then a new political consensus on climate change is achievable based on a risk-based approach, grounded in science, not ideology, that clearly spells out the probability and impact of realistic climate change scenarios.

Alan Dupont is professor of international security at UNSW and a non-resident fellow at the Lowy Institute.

This opinion piece was first published in The Australian.